The present invention relates generally to automatic welding apparatus and more particularly to welding apparatus for welding contact tabs to solar cells. The welding apparatus of the invention is specifically intended for use with solar cells which are utilized in space vehicular solar generators. The apparatus is provided with a plurality of welding electrodes positioned at intervals relative to each other and also positioned relative to a conveying table upon which the solar cells are moved past a welding station at which the welding electrodes are located.
Semiconductor solar cells individually supply voltages which are rather low and usually well below one volt. Accordingly, in an apparatus utilizing such cells, numerous solar units are arranged in series connection as a function of target terminal voltage.
Cells of this type normally measure only a few centimeters taken in the edgewise direction and accordingly they are in electrical conducting interconnection.
Based upon extremely high operational loads and the requirements of functional reliability for solar cells such as those used in space vehicular solar generators, solar cells of this type must be particularly fail safe in their design and structure. More specifically, the junctions of single solar cells where contact tabs consisting of silver are welded onto silver-evaporated back surfaces, there must be provided the utmost dependability since if an error function develops in a single cell it can result in failure or malfunction of an entire series of cells which will produce serious energy problems in space vehicular missions.
Welding is considered to be the preferred method for joining contacts to the solar tabs and it has developed that welding is now preferred to other attachment processes.
Furthermore, in view of the sensitive state of the cells, a key factor favoring utilization of welding as the attachment process relates to the quality of the attachments or connections which are made in that a precise control of parameters such as current, voltage, resistance, welding time, electrode pressure and air gap distance, among others, is possible.
A known example of welding units of the type involved wherein the equipment is provided with an air gap electrode unit is described in UNILAB Welding Report No. 12-203 entitled "Excerpt from a Lecture by H. Zschimmer" dated Sept. 27, 1973 given at the International Electronics Center in Munich, Germany.
A drawback of welding units of this type is that they require considerable manual labor. Each welding point must be positioned beneath the electrode by a manual operation which requires, for example, in the case of a satellite equipped with six solar cell panels an alignment of 18,000 cells with 10 to 20 welding points.
The monitoring of single welding units is equally complex inasmuch as individual tests will consume more time even with logging omitted and consequently an incomplete final inspection.
Accordingly, it is an object of the invention to produce an automatic welding apparatus which, for the purpose involved, will operate in a fully automatic, monitored and reproducible manner with the apparatus operating to meet design quality standards and the exigencies of space flight technology.